Process for the extraction of cellulose fibers from lignified fibrous material



Patented Apr. 28, 1942 PROCESS FOR THE EXTRACTION OF CELLU- LOSE FIBERS FROM LIGNIFIED FIBROUS J MATERIAL Walter Talbot Kerr, St. Margarets-on-Thames,

England, assignor to Sisal Pulp Syndicate Limited, London, England No Drawing. Application March 24, 1939, Serial No. 264,043. In Great Britain March 29, 1938 4 Claims.

The invention relates to an improved process for the extraction of cellulose from fibrous lignlfied vegetable material. l

The new process may be applied to a wide variety of fibrous lignified vegetable materials such for example as sisal waste, jute waste, i. e. in the form of sacking, New Zealand hemp, linseed fiax straw, cotton linters, various hard and soft pulping' woods, varieties of eucalyptus having an open grained wood and black wattle. These materials must be comminuted unless they are in a fairly finely divided .state such as is the case with flax straw, and in so far as woody materials are concerned, e. g. eucalyptus and black wattle, it is preferred to reduce them 'to the state of wood wool so as to avoid breaking up the long fibres.

The invention makes it possible to remove the lignin from the cellulose without breaking up the epidermal tissue and disseminating it finely throughout the mass of cellulose thereby rendering it difficult to remove the epidermal tissue by mechanical means.

The cellulose fibres which have been freed from their impurities by the process of the invention are suitable for paper pulp. Many of p the starting materials which maybe used are normally regarded as waste products and the invention is therefore of importance in that it provides a process for producing paper pulp from products formerly regarded as useless for this purpose. Furthermore, the process'of the invention is carried out under such mild conditions that the individual fibres are not'brokenup to a great extent, so that if the original cellulose fibres of the selected materials are long fibres,

the original fibre length is retained and the pulp produced is suitable for making very high quality paper.

In the process according to the invention the fibrous material which has been freed from most of the adhering material and dust, e. g. by mechanical means or by retting, is subjected firstly to the action of a weak solution of an alkali hydroxide or carbonate at a temperature not above its boiling point under atmospheric pressure, and is then subjected to the action of a weak aqueous solution of chlorine or of an agent. yielding chlorine.

The following shows how the invention may be practiced with batches of sisal wa'stef In the firststage the waste is packed into an expanded metal cage at a density of approxi mately lbs. per cubic foot. This cage is immersed in an iron tank containing a. solution of density of'2 Twaddell at a temperature of 60 The tank is provided with heating means,

e. g. a steam coil, electric immersion heaters or external heating, and the temperature of the treating solution is maintained at approximately 212 F. The tank maybe provided with means for maintaining a constant liquid level connected to a container for fresh treating solution so that fresh solution is supplied after each treatment of a quantity of sisal waste to replace the quantity of solution used up in the treatment.

- The cage, which may be suspended from above by a chain, remains in the treating solution for about half an hour and from time to time a movement is imparted to the cage so as to force the treating solution through the fibrous mass. It will be appreciated that in large plants the movements into, through and out of the treating solution can be rendered automatic by the use for example of a chain conveyor.

After this treatment the fibre is washed until the treating solution is removed. It may then either be transformed directly to the next stage of the process or be stored under water or be dried off and stored.

In the second stage of the process according to the invention an apparatus (which must be made of or lined with a chlorine-proof material such as a phenol-aldehyde synthetic resin) may conveniently be used comprising an elongated bath with rounded en'ds having a partition extending part of the way along its long axis but not extending to its ends so that a continuous trough of substantially uniform width is left round the partition. This bath is filled to the desired level with an aqueous solution of chlorine or of an agent yielding the same, At one point in the bath a draw-off pipe is provided with a screened inlet at a fixed distance above the level sodium carbonate or caustic. soda made up to a of the floor of the bath and on the opposite side of the partition a rotating horizontal perforated or skeleton drum is provided which drum is slowly rotated about an axis extending across the trough. This drum is formed of or carries on its outside paddles, or bars, and it will be appreciated that when the sisal waste is fed into the trough it will be carried round by the paddles or bars on therotating drum and continuously ousiy mentioned and a measured quantity of chlorine, said mixture of liquid and chlorine being subjected to a whirling movement so as to ensure uniformity of the solution of chlorine.

The solution delivered under the drum has a strength of approximately 1% and is maintained in the bath at' a temperature of about 80 F. It will be appreciated that by this means the fibre is never subjected to the action of an unduly strong solution of chlorine but nevertheless by the constant addition of fresh quantities of chlorine to the treating liquid, it is treatedwith as much chlorine as is required to act upon the lignin.

Preferably the solution of chlorine with which the fibre is treated, is neutralised'or rendered slightly alkaline by addition of an alkali thereto. In this case the treating liquid will be,

strictly speaking, a solution of an agent yielding chlorine rather than a solution of chlorine.

- moved by a refiner screen without difllculty.

The preferred alkali is milk of lime since it is found that chlorine dissolved in milk of lime exercised a more vigorous action upon the lignin of the fibre, while its action upon the cellulose is diminished.

Samples of the fibre may be removed for examination at any stage' in order to determineif it has undergone suflicient treatment.

The operation will usually be: conducted so that the chlorine supply is cut-ofi sometime before the treatment of the fibre is complete. During this time, after the admission of chlorine has ceased, the chlorine remainingin the bath will be used up. Thus for example, it may be that in approximately three hours the amount of chlorine required will have been admitted and admission of chlorine is then stopped. Circulation of the fibre and of the liquid is however continued for another hourwhen the whole of. the chlorine will have been used up. The type of pulp obtained may be modified by the degree of chlorination and may thus be suited to the type of paper which it is desired to manufacture finallyfrom this pulp.

After the chlorination has been terminated the used solution will be drawn off and the mass well washed with clean water. For this purpose the pulp and the water may be'circulated in the same apparatus, by introducing fresh water under the rotating drum. The water removed through the draw-01f pipe will of course be discharged and not recirculated. v

After washing, the pulp is treated with a weak alkaline solution, e. g. a 2% solution of caustic soda, preferably at a temperature of about 212 F., in order to remove the lignin chloride and any trace of chlorine left. It is again washed with water and if a powerful jet of water is used or brisk circulation the treated mass breaks down into the fine cellulose fibres.

The process may also be carried out continuously. The material and the liquid are introduced into the top or first treatment zone along which they pass together and when they reach may be three treatment zones, the first will be used for the first alkaiitreatment and the subsequent washing, the second for the chlorination treatment and washing, and the third for the final alkali treatment and washing. The apparatus may'be suitably made from reinforced concrete and this material will resistthe action of the treating liquid in the chlorinating stage.

For the other blocks however some form of aikali-proof lining is required.

By the treatment according to the invention the reaction of the chlorine is confined to the fine individual fibres consisting of lignified cellulose, and the extraneous matter such as adheringepidermal tissue, thickened ends of leaf etc. is left in such condition that it may be re- In certain cases, however, e, g. when using sisal, linseed flax or New Zealand hemp, it is found that in the final alkali treatment most of the epidermal tissue floats to the surface and it is possible to effect a preliminary separation of this by floating on the surface of the treating liquid a trace of an oil such as cotton-seed oil, in which the epidermal tissue collects. This surface layer is then removed from the treatment liquid by skimming it on.

After screening the pulp may readily be bleached with bleaching powder and it'is found that a particularly small quantity usually of the order of 3% of this agent is required in order to effect proper bleaching.

The eiiiuents from the three stages may be mixed together, and by this method precipitation is effected of substances dissolved therein. The resulting final eiiluent is then a clear, neutral, harmless liquid requiring no further treatment before it'is discharged, while the solid'precipitated residue is a valuable by-product.

What I claim is:

1. A process for the extraction of cellulose fibres suitable for producing paper pulp, from finely divided fibrous .iignocellulose material, which material has beenfreed from most of the adhering material and dust, which process comprises subjecting the material firstly to the action of a weak solution of an alkaline agent selected from the group consisting of alkali hydroxide and alkali carbonate while heating at a temperature not above its boiling point under atmospheric pressure, then washing the material, then subjecting itwhiie in movement to the action of a weak non-acid aqueous solution of chlorine, chlorine being added as required to keep the concentration constant during the greater part of the treatment, then washing the material, subjecting it to a further treatment with a weak solution of an alkaline agent while heatins at a temperature of about its boiling point under atmospheric pressure, washing the material again, and then mechanically separating the undissolved impurities.

2. A process for the extraction of cellulose fibres suitable for producing paper pulp, from finely divided fibrous lignocellulose material, which material has been freed from most of the adhering material and dust, which process comprises subjecting the material firstly to the action of a weak solution of an alkaline agent selected from the group" consisting of alk i hydroxide and alkali carbonate while heat g at a temperature not above its boiling point under atmospheric pressure, then washing the material, then subjecting it while in movement to the action of a weak non-acid aqueous solution containing chlorine which is rendered and maintained substantially neutral by adding milk of lime, chlorine being added as required to counterbalance the using up of the chlorine during the greater part of the treatment to keep the concentration substantially constant, then washing the material, subjecting it to a further treatment with a weak solution of an alkaline agent at a temperature of about its boiling point under atmospheric pressure, washing the material again, and then mechanically separating the undissolved impurities.

3. A process for the extraction of cellulose fibres suitable for producing paper pulp, from finely divided fibrous lignocellulose material, which material has been freed, from most of the adhering material and dust, which process comprises subjecting the material firstly to the action of a weak solution of an alkaline agent selected from the group consisting of alkali hydioxide and alkali carbonate while heating at a temperature not aboveits boiling point under atmospheric pressure, then washing the material, then subjecting it while in movement to the action of a weak non-acid aqueous solution containing chlorine which is rendered and maintained slightly alkaline by adding milk of lime, chlorine being added as required to counterbalance the using up of the chlorine during the greater. part of the treatment centration substantially constant, then washing the material, subjectingit to a further treatment with'a weak solution of an alkaline agent-at a to keep the contemperature of about its boiling point under atmospheric pressure, washing the material again, and then mechanically separating the solved impurities.

4. Process for the extraction of cellulose fibres suitable for producing paper pulp from finely divided fibrous lignocellulose material, which material has been freed, from most of the adhering material and dust, which process comprises subjecting the material firstly to the action of an aqueous solution of an alkaline agent selected from the group consisting of sodium hydroxide and sodium carbonate made up to a-density of approximately 2 Twaddell at a temperature of 60 F., said treatment being carried out while heating at a temperature not above its boiling point under atmospheric pressure, then washing the material, then subjecting it while in movement to the action of a weak aqueous solution of chlorine which has been at least substantially neutralized by the addition of milk of lime, said solution containing approximately 1% of chlorine and being employed at a temperature of approximately 80 F., chlorine being added as required to maintainthe concentration substantially constant during the greater part or the treatment and milk of lime being added to prevent'the solution becoming acid, then washing the material and subjecting it to a further treatment with a weak solution of alkali and then mechanically separating the undissolved impurities.

WALTER TALBOT KER-It. 

